Means to measure pressure in the human blood stream by a number of techniques are known. However, blood pressure alone fails to provide answers to many questions, such as: whether sufficient volume of blood to satisfy body needs is flowing, the condition of arteries and veins, and the existence of partial blockages that reduce blood flow to critical areas of the body. It is only by determining actual rate and volume of flow that the medical practitioner is provided with greater insight into the actual condition of the circulatory system.
The present invention provides means whereby fluid flow in vivo may be readily determined and in general, the invention comprises one or more fiber optic differential fluid-pressure measuring devices each comprising a first optical fiber sensor and means for positioning the first optical fiber sensor in the flow path at the measurement point. If the devices further consist of several optical fiber sensors, each includes a means for positioning the sensor relative to the measuring position and to each other. In each case, a means for forming a fixed or variable constriction in the flow path of the fluid may be employed. Means are associated with the constriction for positioning the associated optical fiber sensor in the flow path of the fluid at the constriction. The device further includes one or more fiber optic interferometers having either a single leg or a pair of legs with means connecting each of the optical fiber sensors in a leg of an interferometer. Radiant energy is directed into the legs of the interferometers and through each of the sensors; and radiant energy detecting means are connected to the interferometers. The fiber optic probe described may be used in a wide range of veins and arteries (large and small). One specific example chosen for illustration will be the measurement of total cardiac output.